1. Field of the Invention
The present invention relates to providing radio (wireless or mobile) data services, such as multimedia broadcast and multicast services (MBMS), in a radio (wireless or mobile) communication system, such as a universal mobile telecommunication system (UMTS), which is the European-type IMT-2000 system. MBMS can be provided to a plurality of users by modifying an existing transport channel (i.e., modify DSCH into a point-to-multipoint DSCH), and/or by establishing two new physical downlink shared channels (i.e., C-PDSCH and D-PDSCH).
2. Description of the Related Art
A universal mobile telecommunication system (UMTS) is a third generation mobile communication system that has evolved from a European standard known as Global System for Mobile communications (GSM), which aims to provide an improved mobile communication service based upon a GSM core network and wideband code division multiple access (W-CDMA) wireless connection technology.
In December 1998, the ETSI of Europe, the ARIB/TTC of Japan, the T1 of the United States, and the TTA of Korea formed the Third Generation Partnership Project (3GPP), which is currently creating a detailed specification for standardizing the UMTS.
The work towards standardizing the UMTS performed by the 3GPP has resulted in the formation of five technical specification groups (TSG), each of which is directed to forming network elements having independent operations. More specifically, each TSG develops, approves, and manages a standard specification in a related region. Among them, a radio access network (RAN) group (TSG-RAN) develops a specification for the function, items desired, and interface of a UMTS terrestrial radio access network (UTRAN), which is a new RAN (i.e., radio interface) for supporting a W-CDMA access technology in the UMTS.
I. Features of a UTRAN
The constituting elements of a UTRAN are: radio network controllers (RNCs), Node-Bs and user equipment (UE), such as a terminal. The RNCs enable autonomous radio resource management (RRM) by the UTRAN. The Node-B is based on the same principles as the GSM base station, being a physical element performing radio transmission/reception with cells. The UMTS UE is based on the same principles as the GSM mobile station (MS).
FIG. 1 depicts the components of a typical UMTS, whereby the UMTS generally comprises, among many other components, user equipment (UE) such as a terminal 10, a UTRAN 100 and a core network (CN) 200. The UMTS uses the same core network as that of general packet radio service (GPRS), but uses entirely new radio interfaces.
The UTRAN 100 includes one or more radio network sub-systems (RNS) 110, 120. Each RNS 110, 120 includes a radio network controller (RNC) 111, 121 and one or more Node-Bs 112, 113, 122, 123 managed by the RNCs 111, 121.
The RNCs 111, 121 perform functions such as assigning and managing radio resources, and operate as an access point with respect to the core network 200.
The Node-Bs 112, 113, 122, 123, which are managed by the RNCs 111, 121, receive information sent by the physical layer of a terminal 10 (e.g., mobile station, user equipment and/or subscriber unit) through an uplink (UL: from terminal to network), and transmit data to a terminal 10 through a downlink (DL: from network to terminal). The Node-Bs 112, 113, 122, 123 thus operate as access points of the UTRAN 100 for the terminal 10.
The core network 200 comprises, among other elements, a mobile switching center (MSC) 210 for supporting circuit exchange services, a gateway mobile switching center (GMSC) 220 for managing connections with other circuit switched networks, a serving GPRS support node (SGSN) 230 for supporting packet exchange services, and a gateway GPRS support node (GGSN) 240 for managing connections with other packet switched networks.
A primary function of the UTRAN 100 is to establish and maintain a radio access bearer (RAB) for a call connection between the terminal 10 and the core network 200. The core network 200 applies end-to-end quality of service (QoS) requirements to the RAB, and the RAB supports the QoS requirements established by the core network 200. Accordingly, the UTRAN 100 can satisfy the end-to-end QoS requirements by establishing and maintaining the RAB.
The RAB service can be further divided into lower conceptual levels, namely, into an Iu bearer service and a radio bearer service. The Iu bearer service handles reliable user data transmissions between boundary nodes of the UTRAN 100 and the core network 200, while the radio bearer service handles reliable user data transmissions between the terminal 10 and the UTRAN 100.
The data service provided to a particular terminal 10 is divided into circuit switched (circuit exchanged) service and packet switched (packet exchanged) service. For example, typical voice telephone service falls under circuit switched service, while web-browsing service via an Internet connection is classified as packet switched service.
To support circuit switched service, the RNC 111, 121 connects with the MSC 210 of the core network 200, and the MSC 210 connects with the GMSC 220 that manages connections coming from or going out to other networks.
For packet switched service, the SGSN 230 and the GGSN 240 of the core network 200 provide appropriate services. For example, the SGSN 230 supports the packet communication going to the RNC 111, 121, and the GGSN 240 manages the connection to other packet switched networks, such as an Internet network.
II. Various UTRAN Interfaces
Between various network structure elements, there exists an interface that allows data to be exchanged for communication therebetween. The interface between the RNC 111, 121 and the core network 200 is defined as the Iu interface. The Iu interface is referred to as “Iu-PS” if connected with the packet switched domain, and referred to as “Iu-CS” if connected with the circuit switched domain.
Various types of identifiers are required to maintain proper connections between the terminals 10 and the network (UTRAN 100 and core network 200). A description regarding a radio network temporary identifier (RNTI) will be made herebelow. The RNTI uses identification (discrimination) data of the terminal 10 while a connection between the terminal 10 and the UTRAN 100 is maintained. To do so, four types of RNTI, namely, a serving RNC RNTI (S-RNTI), a drift RNC RNTI (D-RNTI), a cell RNTI (C-RNTI), and a UTRAN RNTI (U-RNTI) are defined and used.
The S-RNTI is allocated by a servicing RNC (SRNC) when a connection between the terminal 10 and the UTRAN 100 is established, and this becomes the data that allows discernment of the corresponding terminal 10 by the SRNC. The D-RNTI is allocated by a drift RNC (DRNC) when handovers between RNCs 111, 121 occur in accordance with the movement of the terminal 10. The C-RNTI is the data that allows discernment of a terminal 10 within the controlling RNC (CRNC), and a terminal 10 is allocated a new C-RNTI value from the CRNC whenever the terminal 10 enters a new cell. Finally, the U-RNTI comprises an SRNC identity and an S-RNTI, and because the SRNC manages the terminal 10 and because discernment data of a terminal 10 within the corresponding SRNC can be known, the U-RNTI can thus be considered to provide the absolute discernment data of a terminal 10.
When transmitting data using a common transport channel, a C-RNTI or a U-RNTI is included in the header of the medium access control (MAC) protocol data unit (MAC PDU) at the MAC-c/sh layer. At this time, a UE identification (ID) type indicator, indicating the type of RNTI that was included, is also included together in the header of the MAC PDU.
For UMTS Terrestrial Radio Access (UTRA), there are typically two types of physical layer signaling methods, namely, TDD (Time-Division Duplex) and FDD (Frequency-Division Duplex). The UTRA FDD radio interface has Logical channels, which are mapped to Transport channels, which are again mapped to Physical channels. Logical channel to Transport channel conversion happens in the MAC (Medium Access Control) layer, which is a lower sub-layer in the Data Link Layer (Layer 2).
In the downlink (DL: from network to terminal), three different types of Transport channels are typically available for data packet transmission, namely the DCH (Dedicated CHannel), the DSCH (Downlink Shared CHannel) and the FACH (Forward Access CHannel).
The DCHs are assigned to single users through set-up and tear down procedures and are subject to closed loop power control that, if used for circuit service such as voice, stabilizes the BER (bit error rate) and optimizes CDMA performance.
The DSCH is a shared channel on which several users can be time multiplexed. No set-up and tear down procedures are required and the physical channel on which the DSCH is mapped does not carry power control signaling. However, since closed loop power control is still required, users that are allowed to access DSCH services must have an associated DCH that is active. The DCH, if not already active due to another transport service, must be activated just to allow the access to the DSCH and to carry physical layer signaling only.
The FACH is shared by several users to transmit short bursts of data, but, unlike the DSCH, no closed-loop power control is exerted and no associated DCH must be activated to access this channel.
For each one of the above channels, different combinations of spreading factor (SF) and code rate can provide the bandwidth and the protection required for different data services and communication environments.
III. UTRAN Protocol Structure
FIG. 2 illustrates a radio access interface protocol structure between the terminal 10 and UTRAN 100 that is based upon the 3GPP wireless access network standards. Here, the radio access interface protocol has horizontal layers including a physical layer, a data link layer and a network layer, and has a user plane for transmitting data information and a control plane for transmitting control signals arranged vertically.
The user plane is a region to which traffic information of a user, such as voice or an Internet-protocol (IP) packet, is transmitted. The control plane is a region to which control information, such as an interface of a network or maintenance and management of a call, is transmitted.
In FIG. 2, protocol layers can be divided into a first layer (L1), a second layer (L2) and a third layer (L3) based upon the three lower layers of an open system interconnection (OSI) standard model that is well-known in the art of communication systems. Each layer shown in FIG. 2 will now be described.
The first layer (L1) uses various radio transmission techniques to provide information transfer service to the upper layers. The first layer (L1) is connected via a transport channel to a MAC (medium access control) layer located at a higher level (precedence), and the data between the MAC layer and the physical layer is transferred via this transport channel.
Data is transmitted according to a transmission time interval (TTI) through the transport channel. The physical channel transfers data upon division into certain units of time, called frames. In order to synchronize the transport channel between the UE (terminal 10) and the UTRAN 100, a connection frame number (CFN) is used. For the transport channels, with the exception of the paging channel, the range of the CFN value is between 0 to 255. That is, the CFN is repeated (circulated) by a period of 256 frames.
Besides the CFN, a system frame number (SFN) is also used to synchronize the physical channel. The SFN value has a range of 0 to 4095 and is thus repeated (circulated) by a period of 4096 frames.
The MAC layer provides a re-allocation service of MAC parameters for allocation and re-allocation of radio (wireless) resources. The MAC layer is connected to an upper layer called a RLC (radio link control) layer through a logical channel, and various logical channels are provided according to the type of transmitted information. In general, when information of the control plane is transmitted, a control channel is used. When information of the user plane is transmitted, a traffic channel is used.
The MAC layer is divided into a MAC-b sublayer, a MAC-d sublayer, and a MAC-c/sh sublayer, according to the type of transport channel being managed. The MAC-b sublayer manages a broadcast channel (BCH) handling the broadcast of various data and system information.
The MAC-c/sh sublayer manages a shared transport channel, such as a forward access channel (FACH), a downlink shared channel (DSCH), or the like, that one terminal shares with other terminals. In the UTRAN 100, the MAC-c/sh sublayer is located in a controlling RNC (CRNC) and manages channels shared by all terminals in a cell, so that one MAC-c/sh sublayer exists for each cell. A MAC-c/sh sublayer also exists in each terminal 10, respectively.
The MAC-d sublayer manages a dedicated channel (DCH), which is a dedicated transport channel for a specific terminal 10. Accordingly, the MAC-d sublayer is located in a serving RNC (SRNC) that manages a corresponding terminal 10, and one MAC-d sublayer also exists in each terminal 10.
A radio link control (RLC) layer provides support for reliable data transmission, and may perform a function of segmentation and concatenation of an RLC service data unit (SDU) coming from a higher layer. The RLC SDU transferred from the higher layer is adjusted in its size according to a throughput capacity at the RLC layer, to which header information is added, and is then transferred to the MAC layer in the form of a protocol data unit (PDU), i.e., a RLC PDU. The RLC layer includes an RLC buffer for storing the RLC SDU or the RLC PDU coming from the higher layer.
The RLC layer may be part of the user plane or the control plane in accordance with an upper layer connected thereto. The RLC layer is part of the control plane when data is received from the RRC layer (explained hereafter), and the RLC layer is part of the user plane in all other instances.
A packet data convergence protocol (PDCP) layer is located at an upper layer from the RLC layer, allowing data to be transmitted effectively on a radio interface with a relatively small bandwidth through a network protocol, such as the IPv4 or the IPv6. For this purpose, the PDCP layer performs the function of reducing unnecessary control information used in a wired network, and this function is called, header compression.
Various types of header compression techniques, such as RFC2507 and RFC3095 (robust header compression: ROHC), which are defined by an Internet standardization group called the IETF (Internet Engineering Task Force), can be used. These methods allow transmission of only the absolutely necessary information required in the header part of a data, and thus transmitting a smaller amount of control information can reduce the overall amount of data to be transmitted.
As can be understood from FIG. 2, in case of the RLC layer and the PDCP layer, a plurality of entities may exist in a single layer thereof. This is because one terminal may have many radio (wireless) carriers, and typically, only one RLC entity and one PDCP entity is used for each radio carrier.
A broadcast/multicast control (BMC) layer performs the functions of scheduling a cell broadcast (CB) message transferred from the core network 200 and of broadcasting the CB message to UEs positioned in a specific cell or cells. At the UTRAN 100, the CB message transferred from the upper layer is combined with information, such as a message ID (identification), a serial number, a coding scheme, etc., and transferred to the RLC layer in the form of a BMC message and to the MAC layer through a common traffic channel (CTCH), which is a logical channel. The logical channel CTCH is mapped to a transport channel (i.e., a forward access channel (FACH)), and to a physical channel (i.e., a secondary common control physical channel (S-CCPCH)).
The radio resource control (RRC) layer located at the lowest portion of the third layer (L3) is only defined in the control plane, and controls the transport channels and the physical channels in relation to the setup, the reconfiguration, and the release (cancellation or tear down) of the radio bearers (RBs). Here, the RB refers to a service provided by the second layer (L2) for data transmission between the terminal 10 and the UTRAN 100. In general, the set up of the RB refers to the process of stipulating the characteristics of a protocol layer and a channel required for providing a specific data service, and setting the respective detailed parameters and operation methods therefor.
Among the RBs, the RB used for exchanging an RRC message or a NAS (Non-Access Stratum) message between a particular terminal 10 and the UTRAN 100 is called a SRB (Signal Radio Bearer). If a SRB is established between a particular terminal 10 and the UTRAN 100, an RRC connection exists between the terminal 10 and the UTRAN 100. A terminal 10 having an RRC connection is said to be in a RRC connected mode, while a terminal 10 without an RRC connection is said to be in idle mode. A terminal 10 in an RRC connected mode is classified, depending upon the channel received, into the states comprising, Cell_PCH or URA_PCH, Cell_FACH, Cell_DCH.
For a terminal 10 in the Cell_DCH state, a dedicated logical channel and a transport channel DCH are established, and the DCH is always received. If a DSCH has been established, the DCH and the DSCH can be received together. For a terminal 10 in the Cell_FACH state, a dedicated logical channel and a transport channel FACH are established, and FACH data can always be received. In the Cell_FACH state, DCH and DSCH cannot be received. For a terminal 10 in the Cell_PCH and URA_PCH states, a dedicated logical channel has not been established. However, in this state, a paging message via the PCH, or a CBS (cell broadcast service) message via the FACH can be received.
Here, URA (UTRAN Registration Area) is an area defined by one or more cells, and provides an efficient method for supporting the mobility of the terminal 10. When a terminal 10 is in the URA_PCH state, the UTRAN 100 does not know which cell the corresponding terminal 10 is located in, but it can be discovered as to which URA region the terminal 10 is located in. Thus, when performing paging, a paging message is transmitted to all cells, which are part of a particular URA region. In contrast, if the terminal 10 is in the Cell_PCH state, because the UTRAN 100 can determine the cell that the terminal 10 is located in, paging messages are only transmitted to those particular cells having a terminal 10 existing therein.
Next, the downlink shared channel (DSCH) will be described in more detail. The DSCH is used to carry dedicated control information or traffic data to a plurality of users who share the channel. Code multiplexing is performed for the plurality of users so that a single channel may be shared. Thus, the DSCH can be defined by a series of code sets.
Unlike in the uplink, the downlink suffers from a code deficiency (i.e., code shortage) problem. This is because there is a limit on the number of codes that a cell can have for a single base station (Node-B). This is related to a spreading factor (SF), and the number of physical channels decreases as the data transmission rate increases. Also, certain types of data services exhibit data burst characteristics. Thus, when only a single channel is allocated continuously, efficient use of codes becomes difficult. Namely, if the DCH is used to carry data having burst characteristics, code shortage problems occur.
To address this problem, a plurality of scrambling codes may be used. However, the use of scrambling codes cannot increase code usage efficiency, and the complexity of the receiving end is undesirably increased.
Alternatively, a method of commonly using (i.e., sharing) a single channel is used, and to do so, code multiplexing is employed. For the physical channel, the basic transmission unit is called a radio frame. Code allocation is performed for each and every radio frame. Thus, a channel code for the physical channel of the DSCH is varied for each and every radio frame.
A physical downlink shared channel (PDSCH), which is a type of physical channel, is used to transport a transport channel, i.e., a DSCH. Namely, the PDSCH is used to carry the DSCH, i.e., the PDSCH is mapped to the DSCH. One PDSCH corresponds to one channelization code. One PDSCH radio frame is allocated to only one particular UE (terminal). The radio network allocates a respectively different PDSCH to a respectively different UE for each radio frame. More than one PDSCH, each having the same SF for a particular radio frame, may be allocated to one particular UE. Each PDSCH is correlated with (i.e., is associated with) one dedicated physical channel (DPCH) and operates for each and every radio frame. Such correlated DPCHs are called associated DPCHs.
The PDSCH and the associated DPCH need not have the same SF. The PDSCH cannot transport physical layer control information, such as Pilot (pilot control), TFCI (Transport-Format Combination Indicator), TPC (Transmitter Power Control), thus all physical layer control information related to the DSCH are carried via a downlink physical control channel (DPCCH) that constitutes an associated DPCH. The UE can decode the DSCH by using the TFCI Field 2 (TFCI2) data carried via the associated DPCH.
Macrodiversity is not applied to the DSCH, and the DSCH is transmitted from only one particular cell. Here, it is understood that “macrodiversity” refers to enabling a mobile station (UE) to communicate with the fixed network by more than one radio link, i.e. a mobile (UE) can send/receive information towards/from more than one radio port (or base station (Node-B)).
UMTS has several different time slot configurations depending upon the channel being used. In the 3GPP standard, a basic transmission unit of the physical channel is a radio frame. The radio frame has a length of 10 ms and is comprised of 15 time slots. Each time slot has fields for transmitting various data bits, such as TFCI. For example, in DPCH downlink and uplink time slot allocation, each slot may have TCP (Transmit Power Control), FBI (Feedback Information) used for closed loop transmission diversity, TFCI containing information related to data rates, and pilot bits, which are always the same and are used for channel synchronization.
FIG. 3 illustrates a channel coding method for a TFCI that is transmitted via the associated DPCH. In general, TFCI (which is 10-bit data) are encoded into 30-bit data through channel coding, and transmitted via a TFCI field in each and every frame. However, for the DPCH, which is an associate or a counterpart (complement) to the DSCH, TFCI division (partition) mode channel coding is employed as shown in FIG. 3. Here, the 5-bit data at each input terminal refers to a first TFCI field data and a second TFCI field data, respectively. The first TFCI field provides the transmission format association data of the transport channel DCH that is mapped to the DPCH. In contrast, the second TFCI field provides the transmission format association data of the associated DSCH, and the channel code data. Each of the 5-bit TFCI field data is encoded into two 16-bit TFCI code words via the respectively different bi-orthogonal code encoders. The data that has been encoded into two 16-bit TFCI code words through channel coding, is mixed together with one TFCI field that constitutes a radio frame and then arranged (distributed).
FIG. 4 illustrates a protocol model for the DSCH when there is an Iur interface, which is an interface between the SRNC and the CRNC. On the downlink, logical channels that are mapped to the DSCH include a DTCH (dedicated traffic channel) that is used to carry data for a particular UE, and a DCCH (dedicated control channel) that is used to carry signaling data (e.g., RRC messages) for a particular UE. In practical use, the DSCH is mainly used for carrying DTCH data. The RLC modes for the DSCH include an answer mode or a non-answer mode. The DSCH always operates together with one or more DL DCHs (downlink dedicated channels). The DSCH data transmission scheduling is performed by the MAC-c/sh of the CRNC. The DSCH frame protocol (FP), by adding a header to the MAC-c/sh PDU, creates a DSCH FP PDU that is then transferred to the base station (Node-B).
The DSCH is allowed to transfer to the corresponding terminals (UE), PDSCH OVSF (orthogonal variable spreading factor) code allocation data that are performed at the MAC-c/sh, by employing the TFCI codeword of the associated DPCCH. This is advantageous in efficiently using radio (wireless) resources, for packet data that have a high peak data rate but a relatively low activity cycle. The MAC-c/sh of the CRNC temporarily allocates OVSF (orthogonal variable spreading factor) codes of the PDSCH to the user for each and every frame, whenever packet data transmissions are requested.
FIG. 5 illustrates a DSCH data transfer procedure used in the DSCH FP of the Iub interface, which is an interface between a Node-B and a CRNC. This procedure is used when DSCH data frames are transmitted from the CRNC to the base station (Node-B). The Iub DSCH data stream contains data that is transmitted on a single DSCH for a single UE. For one UE, one or more Iub DSCH data streams may exist. A single Iub user plane transport bearer transmits only one DSCH data stream. Here, a transport bearer refers to a carrier of a wired network existing within the UTRAN that provides data transmission services between an RNC and a base station, or between two different RNCs.
IV. Providing MBMS to Users
Multimedia broadcast/multicast service (MBMS) is a service to provide multimedia data (e.g., audio, images, video) to a plurality of terminals (users) by using a uni-directional point-to-multipoint bearer service. MBMS was newly developed because of the shortcomings in the related art 3GPP wireless access network standards described above. In particular, the related art techniques for establishing various channels and protocol execution have certain limitations and disadvantages in providing multimedia services to users.
For example, employing CBS messages (previously described) is problematic for the following reasons. First, the maximum length of a CBS message is restricted to 1230 octets. Thus, this is not appropriate for use in broadcasting or multicasting multimedia data. Second, because a CBS message is only broadcast to all terminals within a cell, the multicasting of data via a wireless (radio) interface to provide data services to only a particular group of users (terminals) is not possible.
In general, “multicast” refers to transmitting (propagating) data to a specified group of users connected to a local area network (LAN) or the Internet, whereby one user transmits data to a few users, who each then transmit the received data to a plurality of users using a bucket relay method. Unlike “unicast,” which is the transmission of data to one specified user, or “broadcast,” which is the transmission of data to an unspecified plurality of users, multicast is the transmission of data to a specified plurality of users.
In UMTS, the multimedia services to be provided to users are based upon packet switching and Internet access. MBMS refers to a downlink transmission service for providing data services such as, streaming data services (e.g., multimedia, video on demand, webcast) or background data services (e.g., e-mail, short message services (SMS), downloading), to a plurality of terminals by employing a common (dedicated or exclusive) downlink channel.
MBMS can be classified into a broadcast mode and a multicast mode. The MBMS broadcast mode refers to transmitting multimedia data to all users within a broadcast area, whereby a broadcast area refers to a region where broadcast service is possible. Within a single PLMN (public land mobile network), which is any wireless communications system intended for use by terrestrial subscribers in vehicles or on foot, more than one broadcast region may exist, and more than one broadcast service may be provided in one broadcast region. Also, a single broadcast service may be provided to many broadcast regions. The related art procedures for users to receive a certain broadcast service are as follows.
(1) Users receive a service announcement provided by the network. Here, a service announcement refers to providing to the terminal, an index and any related information of the services to be provided.
(2) The network establishes a bearer for the corresponding broadcast service.
(3) Users receive service notification provided by the network. Here, service notification refers to notifying the terminal of the information regarding the broadcast data to be transmitted.
(4) Users receive the broadcast data transmitted from the network.
(5) The network releases the bearer for the corresponding broadcast service.
The MBMS multicast mode refers to the service for transmitting multicast data to a particular user (terminal) group within a multicast area. Here, a multicast area refers to a region where multicast service is possible. Within a single PLMN, more than one broadcast region may exist, and more than one broadcast service may be provided in one broadcast region. Also, a single broadcast service may be provided to many broadcast regions. The related art procedures for users to receive a certain multicast service are as follows.
(1) A user must first subscribe to a multicast subscription group. Here, subscribing refers to establishing a relationship between the service provider and the user (subscriber). A multicast subscription group refers to a group of users who have completed the subscription process.
(2) Users who subscribed to the multicast subscription group receive a network announcement provided by the network. Here, a service announcement refers to providing to the terminal, an index and any related information of the services to be provided.
(3) A user who subscribed to a multicast subscription group must join a multicast group in order to receive a particular multicast service. Here, a multicast group refers to a group of users receiving a particular multicast service. Joining refers to one user merging with the other users in a multicast group who congregated to receive a particular multicast service. Joining is also referred to as MBMS multicast activation. Thus, a user can receive particular multicast data through MBMS multicast joining or activation.
(4) The network establishes a bearer for the corresponding multicast service.
(5) A user who joined a multicast group receives service notification provided by the network. Here, service notification refers to notifying the terminal of the information regarding the broadcast data to be transmitted.
(6) Users receive the multicast data transmitted from the network.
(7) The network releases the bearer for the corresponding broadcast service.
MBMS user data (i.e., control information and content data) is transmitted from the RNC 111, 121 to the terminal 10 via a base station (Node-B) by employing services of the user plane of the UTRAN protocol. Namely, the services of the PDCP, RLC, and MAC layers in the user plane, and services of the physical plane are employed to transmit the MBMS user data from the RNC to the terminals (UE) via the base station (Node-B). More particularly, the MBMS user data that is transferred from the CN (core network 200) undergoes header compression at the PDCP layer, and then is transferred to the RLC UM entity via the RLC UM SAP. The RLC UM entity then transfers the data to the MAC layer via a logical channel, i.e., a common (shared) traffic channel. The MAC layer adds a MAC header to the received data and transfers the data to the physical layer in the base station (Node-B) via a common (shared) transport channel. Finally, after further processing, such as coding and modulation at the base station (Node-B) physical layer, data transmission to the terminals via a common (shared) physical channel is performed.
An MBMS RB, which is a radio bearer (RB) for the MBMS, serves to transmit user data of one specific MBMS, transferred from the core network 200 to the UTRAN 100, to a specific terminal group. The MBMS RB is divided into a point-to-multipoint RB and a point-to-point RB.
In order to provide MBMS, the UTRAN 100 selects one of the two types of MBMS RBs. In order to select the MBMS RB, the UTRAN 100 recognizes the number of users (terminals 10) for the specific MBMS existing in one cell. The UTRAN 100 internally sets a threshold value, and if the number of users existing in a cell is smaller than the threshold value, the UTRAN 100 sets a point-to-point MBMS RB, whereas if the number of users existing in a cell is greater than the threshold value, the UTRAN 100 sets a point-to-multipoint MBMS RB.